The present invention relates to a combined bearing and sensor assembly, and in particular to an assembly suitable for use in anti-lock braking systems.
Anti-lock braking systems generally require the use of sensors located close to individual bearings to monitor the speed of rotation of the bearings, for example, by measuring the speed at which the outer race rotates relative to a shaft on which both the sensor and the inner race of the bearing are mounted. A typical sensor and bearing assembly of this type has a tone ring which is connected to, and rotates with, the outer race. The tone ring has a number of separate regions (for example magnetized regions) evenly spaced about the tone ring which are detectable as they pass close by the sensor. The frequency with which these regions are detected by the sensor can then be used to determine the speed of rotation of the outer race of the bearing. In practice, the rotation of the tone ring close to the sensor causes the sensor to generate an electrical signal whose frequency is proportional to the angular velocity of the tone ring and hence the outer race.
It is generally preferred to use as small a sensor as possible so as to minimize the total size of the combined bearing and sensor assembly. However, it has been discovered that if a small sensor is used, the air gap between the sensor and the tone ring must be very small and must be maintained at a specific thickness with only a very small acceptable margin before the separation becomes too large or too small; that is to say the gap between the sensor and the tone ring must be maintained to a very close tolerance. It has also been discovered, somewhat surprisingly, that even if the sensor is held in place with a coupling ring which engages, for example, a shaft onto which the bearing and sensor are to be mounted with a tight interference fit, the coupling ring, and thus the sensor, may still move axially along the shaft during normal usage of the bearing such that the air gap alters. Where a relatively small sensor is used such movement, and the consequent alteration of the air gap, may be sufficient to adversely affect the operation of the sensor.
Conventionally, sensor units for use in, for example, anti-lock braking systems, have been sold and mounted separately from the bearing assembly. The fact that the sensor unit is separate from the bearing assembly is advantageous because this allows the bearing assembly to be dismounted periodically for maintenance of the bearing assembly. It also has a number of associated disadvantages. Firstly, it requires two mounting steps rather than just the one step involved in mounting a conventional (non-anti-lock braking system) bearing assembly, and the mounting of the two separate units is not straightforward since the gap between the sensor and the tone ring must be very accurately achieved and maintained; secondly, it is inconvenient for vehicle manufacturers who must ensure that the correct sensors are used with the correct bearing units. Manufacturers would generally prefer to buy and mount a combined bearing and sensor assembly. The present invention seeks to provide a combined bearing and sensor assembly and a method of mounting a combined bearing and sensor assembly which overcomes one or more of the disadvantages associated with the prior art discussed above.
According to a first aspect of the present invention there is provided a combined bearing and sensor assembly for mounting on a mounting surface, said assembly comprising a bearing unit which includes sensor unit engaging means, and a sensor unit which includes a sensor coupling ring having bearing unit engaging means, the assembly being characterized by the sensor unit coupling ring further having preferential mounting surface engaging means, whereby said sensor unit engaging means engages with said bearing unit engaging means when said combined bearing and sensor assembly is not mounted on a mounting surface, and said sensor coupling ring engages with the mounting surface in preference to the bearing unit when said combined bearing and sensor assembly is mounted on a mounting surface, said sensor coupling ring engaging the mounting surface by means of said preferential mounting surface engaging means, thus allowing said bearing unit to be dismounted from and remounted onto said mounting surface without removal or substantial disturbance of the sensor unit.
Reference herein to a mounting surface will be understood as reference to any surface suitable for mounting a sensor unit and/or a bearing unit in, on or around, such as is typically found on axles, axle tubes and bearing housings for example.
Ideally, the preferential mounting surface engaging means is connected to the bearing unit engaging means so as to disengage the bearing unit engaging means for the sensor unit engaging means, or, at least, to weaken the engagement, as the combined bearing and sensor assembly is mounted on a mounting surface. In a currently preferred embodiment, the sensor coupling ring is at least in part substantially rotationally symmetrical about a central axis, and includes a generally axially extending first portion, which forms the preferential mounting surface engaging means and whose radially inner surface engages the mounting surface on, for example, an axle or axle tube on which the combined bearing and sensor assembly is to be mounted. In this currently preferred embodiment, a radially inwardly directed lip, the radially inner end of which forms the bearing unit engaging means, is formed on the free end (i.e. the end adjacent to the bearing unit) of the first portion.
The sensor unit engaging means of the bearing unit may take the form of a cooperating surface which is engageable with the bearing unit engaging means, the sensor coupling ring being so constructed and arranged that the bearing unit engaging means is urged radially inwardly into a firm contact with the cooperating surface when the combined bearing and sensor assembly is not attached to a mounting surface on, for example, an axle or axle tube. The first portion is preferably shaped such that when the sensor coupling ring is mounted onto an axle or axle tube, the radially inwardly directed lip is deflected radially outwardly by a small amount such that the engagement between the bearing unit engaging means and the sensor unit engaging means is at least reduced.
The first portion of the coupling ring may be connected to a radially outwardly extending backing portion having an axially directed flange arranged concentrically with the first portion whereby a sensor may be held in place between the flange and the radially outer surface of the first portion.
In order to increase the deflection of the bearing unit engaging means on mounting the coupling ring on a mounting surface, the coupling ring preferably has slits extending axially inwardly from the free end thereof. Furthermore, the coupling ring may include one or more dedicated cam surfaces which cooperate with the mounting surface to increase the radial deflection of the bearing unit engaging means. Typically, the mounting surface on which the combined bearing and sensor assembly is to be mounted will have a slightly tapered free end, and one of the dedicated cam surfaces may advantageously take the form of a radially directly, rounded ring-like protrusion formed adjacent the free end of the preferential mounting surface engaging means, which protrusion engages said tapered portion of the mounting surface. Ideally, the dedicated cam surfaces and the slits are both formed on the sensor coupling ring, their cumulative effects greatly enhancing the operation of the coupling ring.
Preferably, the sensor unit and the bearing unit are so configured that as they are brought together, permanent opposing abutment surfaces formed on the sensor and bearing units abut one another, thus preventing further relative movement of the units toward one another when the air gap between the tone ring and the sensor is of a predetermined size. The opposing abutment surfaces may conveniently be formed on the bearing unit engaging means and the sensor unit engaging means respectively.
Where it is intended that the sensor unit should be dismountable and remountable separately from the bearing unit, the coupling ring may further include stop means to prevent the sensor unit from being pushed too far onto the mounting surface during re-mounting, by engaging with an axially outward facing surface formed on the member, such as an axle or axle tube, onto which the sensor unit is to be remounted, when the sensor unit is in the correct position on the mounting surface. Where the bearing unit engaging means takes the form of a radially directed lip, the axially outwardly facing surface formed on one side of the lip may provide one of the opposing abutment surfaces, while the other side of the lip may provide the stop means.
According to a second aspect of the present invention there is provided a method of mounting a bearing assembly onto a mounting surface comprising the steps of releasably engaging a sensor unit having a sensor to a bearing unit having a tone ring so as to maintain a fixed gap between the sensor and the tone ring, the bearing unit and the sensor unit together forming a combined bearing and sensor assembly, and mounting the combined bearing and sensor assembly on the mounting surfaces, said sensor unit being provided with bearing unit engaging means and the method being characterized in that the sensor unit is further provided with preferential mounting surface engaging means, and in that said method further including the step of deflecting the bearing unit engaging means simultaneously with the step of mounting the combined bearing and sensor assembly, such that the engagement between the sensor unit and the bearing unit is weakened while the engagement between the combined bearing and sensor assembly and the mounting surface is increased, whereby the bearing unit may be dismounted from and remounted onto the mounting surface without disturbing the sensor unit.
Preferably, the mounting surface comprises at least a sensor unit mounting surface portion in, on or around which the sensor unit is mounted, and a bearing unit mounting surface portion, in on or around which the bearing unit is mounted. The bearing unit mounting surface portion could conveniently be axially longer than the sensor unit and thus act as a piloting means for ensuring correct alignment of the sensor unit with respect to the sensor unit mounting surface portion during mounting of the combined bearing and sensor assembly.
According to a third aspect of the present invention there is provided a combined bearing and sensor assembly for mounting on a mounting surface, the assembly comprising a bearing unit including a tone ring and a reference surface having a fixed axial relationship to the tone ring; and a sensor unit including an axial sensor and a sensor coupling ring; the assembly being characterized in that the sensor coupling ring includes an abutment surface, having a fixed axial relationship to the sensor, for abutment with the reference surface, preferential mounting surface engaging means for enabling the bearing unit to be dismounted from and re-mounted onto the mounting surface without removal or substantial disturbance of the sensor unit, and axial anchorage means, wherein the axial anchorage means cooperates with the mounting surface to ensure that the abutment surface of the coupling ring remains in abutment with the reference surface of the bearing unit when the sensor unit and the bearing unit have been correctly mounted even after substantial operation of the combined bearing and sensor assembly, whereby the axial gap between the sensor and the tone ring is maintained substantially constant.
According to the third aspect of the present invention it is not necessary for the bearing unit and the sensor unit to be sold and mounted as a combined unit. However, they cooperate with one another once they have been mounted by means of the abutment between the abutment surface and the reference surface and in this way they may be considered as forming a combined bearing and sensor assembly.
In the present context, the term "axial sensor" refers to a sensor which is axially separated from the tone ring such that a small axial air gap exists between the tone ring and the axial sensor. Radial sensors also exist in which the sensor is radially separated from the tone ring, however, the third aspect of the present invention is not concerned with such arrangements.
The axial anchorage means may cooperate directly with the mounting surface, or alternatively it may cooperate indirectly with the mounting surface of an intermediate member such as a carrier ring.
Preferably the axial anchorage means takes the form of a radially directed lip, or at least one radially directed protrusion, which located, when the combined bearing and sensor assembly is correctly mounted on the mounting surface, between the bearing unit and the mounting surface. Preferably the abutment surface is formed by an outer axially facing surface formed on the axial anchorage means. Where the assembly further incorporates an intermediate member such as a carrier ring, the axial anchorage means preferably locates between the intermediate member and the bearing unit.
The axial anchorage means ideally locates in an end groove formed either in the bearing unit or in the mounting surface (or, where appropriate, in the intermediate member). The end groove preferably extends radially only as far as the radial length of the axial anchorage means, where the majority of the axial stress between the bearing unit and the mounting surface is transmitted by direct abutment between a backface of the bearing unit and an opposing surface of the mounting surface (or intermediate member where appropriate) radially beyond the groove.
Preferably the axial anchorage means includes stop means having a limited amount of give and being adapted to engage the mounting surface (or intermediate member where appropriate) during mounting of the assembly as a result of the abutment between the abutment surface and the reference surface, shortly before the backface of the bearing unit abuts the opposing surface of the mounting surface (or intermediate member where appropriate), wherein the stop means has sufficient give to permit the backface of the bearing unit to continue to move into abutment with the opposing surface of the mounting surface (or intermediate member where appropriate) during mounting of the assembly without damaging the sensor unit, but insufficient give to enable the sensor unit to move axially away from the reference surface during normal usage of the bearing assembly, once the bearing assembly has been correctly mounted. In this way, the stop means acts to take up any excess axial freedom of movement of the sensor unit when the assembly is correctly mounted on the mounting surface. Such freedom of movement may, for example, result from manufacturing the axial anchorage means to have a slightly narrower axial width than the end groove in which it is to locate, so as to allow for small variations in these widths which result from the machining of these features being achievable only to within certain well known tolerances.